In the past, a radar apparatus mounted on a vehicle emits a transmission wave from a transmission antenna and receives a reflected wave from a target, which reflects the emitted transmission wave, at a reception antenna to thus derive a target position and the like with respect to the vehicle (radar vehicle). The detailed processing thereof is as follows. A signal processing unit of the radar apparatus generates a beat signal by mixing a transmission signal corresponding to the transmission wave of which a frequency is changed with a predetermined period and a reception signal corresponding to the reflected wave. That is, the signal processing unit generates the beat signal based on a difference frequency (beat frequency) between the transmission signal and the reception signal in each of an UP section in which the frequency ascends with a predetermined period and a DOWN section in which the frequency descends.
Then, the signal processing unit generates a signal (hereinafter, referred to as a ‘converted signal’) with respect to each frequency by performing FFT (Fast Fourier Transform) for the beat signal. From the converted signals, the signal processing unit extracts a signal exceeding a threshold value of a predetermined signal level as a peak signal. Then, the signal processing unit derives paired data by pairing the peak signal of the UP section and the peak signal of the DOWN section based on a predetermined condition.
For example, the signal processing unit predicts this time paired data (hereinafter, referred to as ‘predicted paired data’) on the basis of the paired data derived in the past, derives a peak signal (hereinafter, referred to as a ‘hysteresis peak signal’) predicting this time peak signal from the predicted paired data and extracts this time peak signal corresponding to the hysteresis peak signal in each of the UP and DOWN sections. Then, the signal processing unit derives paired data from the frequency and angle information of the extracted hysteresis peak signal by pairing the corresponding hysteresis peak signals of the respective sections.
Then, the signal processing unit derives a distance (hereinafter, referred to a longitudinal distance) from the vehicle to the target or a distance (hereinafter, referred to as a transverse distance) of the target with respect to the vehicle in a direction substantially orthogonal to a traveling direction of the vehicle, based on the paired data. Also, the signal processing unit derives a relative speed and angle of the target with respect to the vehicle. Then, the radar apparatus outputs the information on the position, the relative speed and the like of the decided target to a vehicle control device. The vehicle control device performs required vehicle control in accordance with the information of the target. In the meantime, for example, Patent Document 1 discloses a technology relating to the invention.    Patent Document 1: Japanese Patent Application Publication No. 2009-092429A
However, when a plurality of targets exists at the periphery of the vehicle and the reception antenna receives the reflected waves from the plurality of targets at the same time, a plurality of peak signals appears on a frequency axis in the UP and DOWN sections after the FFT processing. Also, not only the peak signals corresponding to the targets but signals due to noises individually appear as the peak signals.
In particular, the peaks signals corresponding to the plurality of targets existing at the same distance from the vehicle appear at the same frequency. Therefore, upon deriving the angle information so as to separate the peak signals, when a reception signal level of a reflected wave from a road side object such as a soundproof wall is higher than a reception signal level of a reflected wave from a preceding vehicle, an angle spectrum of the preceding vehicle is concealed in an angle spectrum of the road side object, so that it may not be extracted. In this case, since the preceding vehicle is not detected, the preceding vehicle that originally exists is regarded as been non-existent, so that the vehicle control device may perform false vehicle control.